Liquid chemicals and water have been blended in predetermined concentrations previously through the use of sensors of both the type which actually engage the liquid, and other electrodeless-type sensors placed in the flow line or container wherein the blended liquid is found.
The use of blended liquid becomes extremely important in industrial applications, such as in the processing of semiconductor wafers, wherein exactly the correct blend of chemical and diluent liquid must be achieved. A wafer processing tool using the blended liquid may cause a substantial amount of waste of semiconductor wafers if the blended liquid does not have the correct concentration of chemical and accordingly, it is desirable that the accuracy of the chemical concentration in the blended liquid be extremely accurate.
Closed loop mixing and blended systems have been known in the past, wherein electrodeless-type sensors have been placed in a storage and mixing tank in some instances, and in other instances, have been placed in a flow duct through which the blended liquid is circulated. In some instances, such electrodeless-type sensors have been placed in series with each other along the flow duct carrying the blended liquid in an attempt to obtain the desired accuracy of measuring the chemical concentration in the blended liquid; however, such electrodeless-type sensors placed in series along the flow duct create such turbulence in the flowing blended liquid that results in measuring the conductivity, and therefore the chemical concentration in the blended liquid, have less than the desired accuracy.
Moreover, the concentrated liquid chemical has been previously pumped and propelled through a line for mixing with the diluent liquid in such a manner that accurate quantities of chemical concentrate cannot be accurately dispensed.